Resonant cavity device



E. G. UNDER RESONANT CAVITY DEVICE Aug. 18, i942. n2,29351 Filed Oct. 8,1940 @ITM *25 \7 BEHWNG v osc/LL/WOH Snnentor nder Patented Aug. 18,1942 UNI' BESONANT CAVITY DEVICE Ernest G. Linder, Philadelphia, Pa.,assignor to Radio Corporation of America, a corporation of DelawareApplication October 8, 1940. Serial No. 360,310

9 Claims.

This invention relates to ultra high frequency devices, and moreparticularly to an ultra high frequency resonant cavity device forgenerating, detecting or converting oscillations into currents of lowfrequency.

The term "ultra high frequency oscillations is generally applied toelectromagnetic oscillations having a frequency of the order of 500megacycles per second and upward. At the higher frequencies, forexample, 3000 megacycles, it has been dimcult to generate powerfuloscillations and equally dimcult to detect eiciently. This dimculty hasbeen mainly due to the space characteristics of the thermionic tubeswhich are employed.

Among the prior art devices are the magnetron and Barkhausen-Kurz tubes.In these tubes, the radio frequency potentials are applied to theelectrodes by means of resonant circuits.

The diiculties of generating or detecting radio frequency oscillations,of a wave length of the order of 10 centimeters, will be appreciated byconsidering the physical size of a magnetron oscillator in which theanode is a cylinder of the order of 2 millimeters radius and 1centimeter length. In this arrangement, the anode is subjected tointense heat when even low power oscillations are generated. Thus it isquite apparent that the space limitations of the prior art oscillatorshave prevented the generation of more than about 10 watts of ultra highfrequency oscillatory energy. Furthermore, devices of the aforementionedtype are inemcient detectors.

(Cl. 25o-20) connected by resonant circuits and which do not themselvesoscillate, but which direct electrons through a resonant cavity. Inother words, the radio frequency potentials will not be applied to thetube elements and thus some of the restrictions on size 'will beeliminated. As an object of this invention, means will be provided forutilizing a resonant cavity to generate, detect or convert oscillationsof a predetermined frequency. It is another object of the invention toprovide a resonant cavity having a size corresponding to a predeterminedband of wave lengths. It is a further object of the invention to providemeans for collecting or inducing electromotive forces within a resonantcavity. A still further object is to provide means for detecting andregenerating ultra high frequency oscillations.

The invention will be described by referring to the accompanying drawingin which Figure 1 is a schematic diagram of one embodiment of theinvention; and Figure 2 is a schematic dlagram' employed in describingthe operation oi the device. I

Referring to Fig. 1, the elements of the thermionic device are suitablysupported within an evacuated envelope I. These elements are: a cathode3, cylindrical focusing elements 5, 1, phasing electrodes 9, Il, acollecting electrode I3 and a hollow resonant cavity I2 includingapertures I5 which are preferably coaxlally mounted between the phasingelectrodes 9 and Il. A dipole antenna Il may beconnected to atransmission line IS which includes a loop 2| arranged within the thecavity I2 for inducing or collecting ultra high frequency energy. The yresonant cavity I2 is preferably but not necessarily of toroidal form sodimensioned that an electromagnetic field of the proper frequency willresonate the cavity and -will establish therein oscillations. Thefrequency, at which resonant oscillations occur, is determined primarilyby the dimensions of the cavity. 'I'he cavity is preferably bounded by asuitable conductor which includes one or more apertures through whichelectrons are directed. By way of an analogue, a Helmholtz resonator forsound waves corresponds to the instant resonant cavity forelectromagnetic waves. If the device is to be use d to convert the ultrahigh frequency energy by means of a-beating oscillator, the currents ofthe beating frequency may be induced within thel cavity I2 by loop 23terminating a transmission line 25 connected t0 a beating oscillator 2l.The cathode, f ocusingand phasing electrodes, and resonant cavity aresuitably biased by connections to a potentiomer 29 which is connectedacross a power source 3l. The collecting electrode I 3 is connected toan am'plier or signal indicating device by a blocking capacitor 33. Thecollecting electrode I3 may be biased slightly positive or slightlynegative by means of the potentiometer 35 and battery 31.

In the operation of the device, an electron beam is established by thecathode 3 and focusing electrodes 5, l. It should be understood that thefirst phasing electrode 9 may also focus the beam. This beam isprojected through the resonant cavity I2 in which the ultra high fre-A'quency iield imparts velocity variation to the beam. Some of thehigher velocity electrons pass through the cavity and reach thecollecting are reversed and returned to the cavity, again passingthrough it. 'I'he phase of the returning electron groups is adjusted byproper. electrode spacing and potential so as to establish oscillationswithin the cavity, or to increase the amplitude of the oscillations, ifoscillations have been established within the cavity.

If the device is` being used as a detector, the waves to be detected areimpressed upon the dipole antenna il and hence induced within thecavity, where they.v form resonant waves which are reinforced orincreased by the regenerative action of the velocity modulated electronbeam. If the device is used as an oscillator for the production of powerat ultra high frequencies, the power is derived by the currents inducedin the loop 2l.

By way of example, the following table ci resonator voltages was foundto give the detection maxima:

V AV MeanV This series/is explainable on the basis of transit time fromthe resonator center to the plate and return. This time I is given by:

This 3/2 power law is followed by the above data.

Putting V=1000, AV=170, S=2.4, we get AT=2.17 -10, experimental value is31610-10. Also These results indicate that transit times of an `integralnumber of periods give maximum sensi- Hence, if the spacing through thecavity is made twice that from the cavity to the cathode and/or anode,then, when the transit time through the cavity is one-half period, thetransit time from cavity to A or to C and back to the cavity will be oneperiod.

Thus, the invention has been described as an ultra high frequencyresonant cavity device in which oscillations may be generated ordetected. Furthermore, the detection may 'be of a regenerative characterwhich increases the eciency of detection about 10 times.

It should be understood that the invention is not limited tothe precisearrangement or spacing of the elements shown.

I claim as my invention:

l. An ultra high frequency device including a source of electrons, acollecting electrode, a resonant cavity positioned between said sourceand said electrode, means for directing electrons from said sourcethrough said cavity and toward said collecting electrode, means foradjusting the phase of the electrons passing through said cavity so thatvelocity variations are established, and a hollow electrode disposedbetween said cavity and collecting electrode electrically biasedindependently of said cavity and said collecting electrode for returningto the cavity the said passing electrons and for adjusting the phase ofelectrons returning through said cavity so that the returning electronsestablish ultra high frev quency Waves within the cavity.

2. An ultra high frequency device including a source of electrons, acollecting electrode, a resonant cavity located between said source andsaid electrode, means for establishing ultra high frequency waves withinsaid cavity, means for directing electrons from said source through saidcavity and toward said collecting electrode, means for adjusting thephase of the electrons passing through said cavity so that velocityvariations are established, and a hollow electrode disposed between saidcavity and collecting electrode electrically biased independently ofsaid cavity and said collecting electrode for returning to the cavitythe said passing electrons and for adjusting the phase of electronsreturning through said cavity so that the returning electrons increasethe amplitude of the ultra high frequency waves established within thecavity.

3. An ultra high frequency device including a source of electrons, acollecting electrode, a resonant cavity located in operable relationbetween said source and said electrode, means for directing electronsfrom said source through said cavity and toward said collectingelectrode, means for adjusting the phase of the electrons passingthrough said cavity so that velocity variations are established, ahollow electrode disposed beresonant cavity operably located betweensaidv source and said electrode, means for establishing ultra highfrequency waves within said cavity, means for directing electrons fromsaid source through said cavity and toward said collecting electrode,means for adjusting the phase of the electrons passing through saidcavity so that velocity variations are established, a hollow electrodedisposed between said cavity and collecting electrode electricallybiased independently of said cavity and said collecting electrode forreturning to thecavity the said passing electrons v and for adjustingthe phase of electrons returning through said cavity so that thereturning electrons increase the amplitude of the ultra high frequencywaves established within the cavity, and means including' saidcollecting electrode for deriving currents corresponding to said waves.

5.. An ultra high frequency device. including a source of electrons, acollecting electrode,l a resonant cavity in operable relation betweensaid source and said electrode, means for establish- .tween said cavityand collecting electrode elecing within said cavity ultra high frequencywaves to be detected, means for applying beating oscillations to saidcavity,.means for directing electrons from said source through saidcavity and toward'said collecting electrode, means for adiusting thephase of the electrons passing through said 'cavity so that velocityvariations are established, a hollow electrode disposed between saidcavity and collecting lelectrode electrically biased independently ofsaid cavity and said collecting electrode `for returning to -said cavitysaid passing electrons and for adjusting the phase of electronsreturning through said cavity, and means including said collectingelectrode for deriving currents having al frequency corresponding to thebeat frequency of the ultra high frequency waves and beatingoscillations,

6. An ultra high frequency device vincluding a source of electrons, acollecting electrode, a resonant cavity operably located between saidsource and said electrode, .means for directing electrons from saidsource through said cavity and toward said collecting-electrode, and ahollow electrode disposed between said cavity and collecting electrodeelectrically biased independ- 'ently of said cavity and said collectingelectrode for returning to said cavity said electrons directed throughthe cavity and for adjusting the Y phase of electrons returning throughsaid cavity so that the returning electrons increase the ultra highfrequency waves established within the cavity by electrons passingtherethrough.

7. An ultra high frequency device including a.

source of electrons, a collecting electrode, a resonant cavity operablylocated between said source and said electrode, means for establishingultra high frequency waves within said cavity,

means for directing electrons from said source through said cavity andtoward, said collecting electrode, and a hollow electrode disposedbetween said cavity and collecting electrode electrically biasedindependently of said cavity and f said collecting electrode forreturning to said cavity said electrons directed throughthe cavity andfor adjusting the phase of electrons returning through said cavity sothat the `returning electrons increase the ultra high frequency wavesestablished within the cavity.

8. Anultra high frequency device including a source of electrons, acollecting electrode, a resonant cavity positioned between said sourceand said electrode, means for directing electrons from vsaid sourcethrough said cavity and toward said collecting electrode, a hollowelectrode disposed between said cavity and collecting electrodeelectrically biased independently of said cavity and said collectingelectrode for returning to said cavity the electrons directedtherethrough' and for adjusting the phase of electrons' returningthrough said cavity so that the returning electrons increase theamplitude of the ultra high frequency waves established within thecavity by electrons passing therethrough,- and means including saidcollecting electrode for deriving currents corresponding to said waves.

9. An ultra high -frequency device including a source oi electrons, acollecting electrode, a

resonant cavity positioned between said sourcel and said electrode,means for establishing ultra high frequency waves within said cavity,means for directing electrons from said source through said cavity andtoward said collecting electrode, a hollow electrode disposed betweensaid cavity and collecting electrode electrically biased independentlyof said cavity and said collecting electrode for returning to saidcavity the electrons directed therethrough and for adjusting the phaseof electrons returning through said cavity so that the returningelectrons increase the ultra high frequency waves established within thecavity, and means including said collecting electrode for derivingcurrents corresponding to said waves.

ERNEST G,.I`.INDER.

